1. Field of the Invention
The present invention relates to coffee roasting equipment, and more particularly to upgrades to existing coffee roaster equipment that will restore and lengthen their service lives.
2. Description of Related Art
Coffee beans were once roasted in open pans held over fires to prepare them for grinding and use in making coffee to be drunk. The first commercial roasters were set into brick kilns that would hold and contain heat from a wood-fired source. Cast iron drum roasters were also used. Conductive heat transfer is used almost exclusively to roast coffee. The coffee picked up heat by direct contact with the hot metal surfaces of the roaster.
Roasting of this type offered little control. Coffee was often roasted too dark, and was very uneven in the degree of roast from bean to bean, since all the coffee could not possibly have the same amount of contact with the hot metal surfaces of the roaster. Jabez Burns invented a roaster in the 1870's that used a perforated metal drum. Such allowed the chaff to separate and convective air flows to circulate around each bean. Hot convective air and radiant heat from the burners and hot metal of the roaster all heated the coffee. Coffee could be roasted evenly, and also much lighter. The benefit of roasting lighter was that the coffee lost less weight in the roasting process, and more salable product emerged from the drum than was possible before.
The new convective system also allowed a longer roast time and better control of the degree of roast. An experienced operator could produce the same roast time and time again, effectively dumping the batch into a stationary cooling bin with an agitator, whereas previous roasters dumped coffee into moving cooling bins wheeled about the factory with no agitation.
The Burns Roaster (Jaebez Burns, Inc., Memphis, Tenn.) was first produced and marketed in 1915. Many roasting operations still prefer this type of batch roaster over more modern ones. So there has evolved a business in restoring and refurbishing the Burns Roasters and others.
Batch roasters can roast 500–600 pounds of green coffee beans at a time, and controlling the roasting temperatures and times is very important in getting good results. Batch drum coffee roasters have either solid drums with convective air flow control, or perforated drums. Roasters now have better flame controls and thermocoupled temperature monitoring, but the progression of the roast is built into the equipment, determined by the metals used, the burners installed, and the cooling system.
For the first few minutes of roasting, the coffee beans stay green, then turn a lighter yellow and emit a grassy smell. The beans start to steam as their internal water content dissipates. Such steam becomes fragrant. A “first crack” will sound off as the real roasting starts to occur. Sugars begin to carmelize, bound-up water escapes, the structure of the bean breaks down, and oils migrate from pockets outward. After the first crack, the roast can be considered complete any time according to taste. The cracking is an audible cue, and it, the look, and smell will all indicate the stage of the roast to an operator.
With darker roasts, carmelization continues, oils migrate, and the beans expand in size as the roast gets darker. Then a “second crack” will be heard, more energetic than the first. Small pieces of bean may be blown away as shrapnel. As the roast becomes very dark, the smoke given off will be more pungent as the bean structure breaks down and the sugars burn. If the sugars are allowed to burn completely, the roast will be ruined.
More specifically, the light brown stage typically occurs at 250–300° F. internal bean temperature. The coffee will have a toasted grain or baked bread smell. Up until first crack the coffee is undergoing an endothermic reaction, taking on heat, but as it undergoes first crack the reaction becomes exothermic, releasing heat/energy. The first crack begins at a 355° F. internal bean temperature. A city roast is achieved at a 400–415° F. A full city roast is had at a 415–425° F. internal bean temperature. For Vienna roast, a 450–465° F. is needed. A full French roast or Italian roast is reached at 475–510° F. internal bean temperature. Sugars are heavily caramelized and begin to be degraded. The woody bean structure carbonizes, the seed continues to expand and loose mass, and the flavor body of the resulting beverage will be thinner and lighter because the aromatic compounds, oils, and soluble solids are burned out of the coffee as smoke. A Spanish roast, with a 520–530° F. internal bean temperature, gets very close to flashing into a fire. Beyond this, the coffee's flavor-contributing compounds will be severely degraded because the cellular matrix of the coffee is completely ruptured, and the soluble solids content of the coffee is vaporized, e.g., a “third crack”.